Filter for electrostatographic developer

ABSTRACT

IMPROVED FILTER FOR SEPARATING AN ELECTROSTATOGRPAHIC DEVELOPER MATERIAL (TONER) WHEREIN THE FILTER MATERIAL IS COATED WITH A PLASTICIZER FOR THE TONER. THE FILTER IS PREFERABLY FORMED FROM FIBER GLASS AND IS COMPRISED, IN THE DIRECTION OF FLOW, OF A LOOSELY ASSEMBLED WEB OR MAT OF INCREASING DENSITY AND A LOOSELY ASSEMBLED WEB OR MAT OF SUBSTANTIALLY UNIFORM DENSITY. THE FILTER IS GENERALLY EMPLOYED IN THE CLEANING STATION OF A XEROGRAPHIC MACHINE AND IS EMPLOYED TO REMOVE TONER PARTICLES SUSPENDED IN AN AIR STREAM. THE FILTER BAG HAS BEEN FOUND TO HAVE A USEFUL LIFE OF 18,000 COPIES OR MORE, AS COMPARED TO CONVENTIONAL FILTER BAGS WHICH HAVE A USEFUL LIFE OF ABOUT 4,000 COPIES.

Mam}! 7 c. F. CLEMENS r 3,570,224

FILTER FOR ELECTROSTATOGRAPHIC DEVELOPER Filed Nov. 17, 1969 INVENTOR.

Carl F. Clemens ATTORNEYS United States Patent 3,570,224 FILTER FOR ELECTROSTATOGRAPHIC DEVELOPER Carl F. Clemens, Webster, N.Y., assignor t0 Xerox Corporation, Rochester, NY. Filed Nov. 17, 1969, Ser. No. 877,240 Int. Cl. Bllld 46/02 US. Cl. 55374 3 Claims ABSTRACT OF THE DISCLOSURE Improved filter for separating an electrostatographic developer material (toner) wherein the filter material is coated with a plasticizer for the toner. The filter is preferably formed from fiber glass and is comprised, in the direction of flow, of a loosely assembled web or mat of increasing density and a loosely assembled web or mat of substantially uniform density. The filter is generally employed in the cleaning station of a xerographic machine and is employed to remove toner particles suspended in an air stream. The filter bag has been found to have a useful life of 18,000 copies or more, as compared to conventional filter bags which have a useful life of about 4,000 copies.

This invention relates to electrostatography and more particularly to a filter for separating electrostatographic developer material (toner). Still more particularly, this invention relates to the separation of toner particles from an air exhaust system employed in a plate-cleaning station of a xerographic machine.

Xerography is the most highly developed electrostatographic process and in the process of xerography, for example, as dislosed in Carlson Pat. 2,297,691 issued Oct. 6, 1942, a xerographic plate, comprising a photoconductive insulating material on a conductive backing, is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the light intensity which reaches them and thereby creates an electrostatic latent image on or in the plate coating.

Development of the electrostatic latent image is usually effected by an electrostatically attractable material, which is generally a thermoplastic resin in the form of finely divided particles usually in the size range from 3 to 20 microns, commonly referred to as toner. In the development of the electrostatic latent image, the toner is brought into surface contact with the coating and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. The developed image is then transferred to a suitable support material, such as paper, and fused thereon to make a permanent image. In the xerographic transfer step substantially all of the resin material or toner is caused to adhere to the support material to form the images thereon, but usually a very small percentage of the resin material or toner remains on the xerographic plate.

The small quantity of resin material or toner remaining on the xerographic plate will affect future operating steps of the xerographic process and if left remaining thereon has an accumulative effect in that additional toner adheres more readily to the xerographic drum in both image and non-image areas thereon.

As disclosed in the Turner et al. latent 2,751,616, issued June 26, 1956, a rotating brush in peripheral contact with the surface of the Xerographic plate may be used to clean the xerographic plate of any residual resin material or toner adhering thereon. The brush, in turn, may be cleaned by a flicking bar disclosed in the above-referenced patent and by a vacuum system similar in structure to that of the common household vacuum cleaner whereby dust that is, residual resin material or toner, is entrained in air and then filtered out from the air by a suitable filter.

The filters presently employed in xerographic machines have a useful life of about 4,000 prints and an improvement in the effective life of these filters, for example, to about 18,000 prints or more is highly desirable.

SUMMARY OF THE INVENTION An object of this invention is to provide for improved filtering of toner particles.

Another object of this invention is to provide an increase in the eifecitve life of filters employed for separating toners.

A further object of this invention is to improve the filters employed in the cleaning station of a xerographic machine.

These and other objects of the invention should be more readily apparent from the following detailed description of the invention.

In brief, the objects of this invention are accomplished by providing a filter for an electrostatographic developer (toner) having at least a portion thereof coated with a plasticizer for the resinous material of the toner. The plasticize causes the toner to lose its particulate shape and spread out over the filter, thereby increasing the effective filtration area.

DESCRIPTION OF THE DRAWING The drawing is a diagrammatic view, partly in section, of the cleaning station of a xerographic machine wherein a filter of the invention is used.

DETAILED DESCRIPTION OF THE INVENTION The filter to be employed for separating the toner is coated or impregnated with a material which causes the resinous material of the toner to lose its particulate shape; i.e., a plasticizer. The plasticizer may be any one of the wide variety of liquid plasticizers which are generally known to plasticize the resinous materials used in formulating toners, with the only limitation being that the plasticizer should not interact with the filter material and be non-volatile under the operating conditions of the filtration. As representative examples of resins which may be employed as the resinous material of the toner there may be mentioned: gum copal, gum sandarac, rosin, cumaroneindene resin, asphaltium, gilsonite, phenol-formaldehyde resins, rosinmodified phenol formaldehyde resins, methacrylate and acrylate resins, polystyrene resins, polypropylene resins, epoxy resins, polyethylene resins and mixtures thereof. Various toners are described in US. Patents 2,659,670; 2,753,308; and 3,079,342.

As representative examples of plasticizers which may be employed to coat a filter for toner, there may be mentioned: abietic acid derivatives, such as methyl abietate; adipic acid derivatives, such as, di-n-hexyl adipate, dicapryl adipate, di(2-ethylhexyl) adipate etc.; benzoic acid derivatives, such as, diethylene glycol dibenzoate, dipropylene glycol dibenzoate, etc.; chlorinated biphenyls; citric acid derivatives such as, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, etc.; lauric acid derivatives, such as, butyl laurate, 1,2-propylene glycol monolaurate, ethylene glycol monoethyl ether laurate, ethylene glycol monobutyl ether laurate, glycerol monolaurate, etc.; oleic acid derivatives, such as methyl oleate, n-propyl oleate, isopropyl oleate, etc.; chlorinated paraffins; phosphates, such as, triethyl phosphate, tributyl phosphate, etc.; phthalic acid derivatives, such as, butyl iso-hexyl phthalate, di-octyl phthalate, -di-n-octyl phthalate, dioctyl isophthalate, di-isoctyl phthalate, diisoctyl isophthalate, dicapryl phthalate, mixed alcohol phthalate, mixed normal alcohol phthalate, di-(Z-ethylhexyl) phthalate, dinonyl phthalate, n-octyl-n-decyl phthalate, etc., sebacate acid derivatives, such as, dimethyl sebacate, diethyl sebacate, dibutyl sebacate, dioctyl sebacate, diisooctyl sebacate, di-normal-butyl isosebacate, dibutoxyethyl sebacate, dibenzyl sebacate, etc., and the like.

The choice of a plasticizer to be employed with a particular filter for separating a particular toner is deemed to be well within the scope of those skilled in the art and, therefore, the scope of the invention is not limited by the hereinabove mentioned illustrative materials. The filter may be produced from any one of a wide variety of filter materials, such as, fiber glass, steel wool, polyethylene fibers, and the like, with fiber glass generally being preferred. The choice of a particular filter material for a specific operation is well within the scope of those skilled in the art and, therefore, no detailed enumeration thereof is deemed necessary for a full understanding of the invention.

The filter material is preferably coated or impregnated with the plasticizer prior to forming the filter and such coating may be effected by any one of a wide variety of procedures, such as for example, spraying the plasticizer onto the material, dipping the material into the plasticizer, etc. The particular method employed for coating or im-. pregnating the filter material is deemed to be Within the scope of those skilled i the art and, therefore, no detailed description thereof is deemed necessary for full understanding of the invention. The plasticizer is preferably applied in an amount to uniformly coat the filter material to be employed as the plasticized portion of the filter in that such uniform application maximizes the useful life of the filter by maximizing the area on which the toner may be retained on the filter in a plasticized state. It is to be understood, however, that other than uniform applications of the plasticizer are contemplated within the spirit and scope of the invention with a corresponding decrease in effectiveness.

The preferred filter, as hereinabove mentioned, is formed of fiber glass, and more preferably is comprised of two sections or walls wherein the stream carrying the toner material initially passes through a first section or wall comprised of a loosely assembled web or mat of progressively increasing density and then through a second section or wall comprised of a loosely assembled web or mat of substantially uniform density having a density which is greater than the maximum density of the first section. In such a filter, only the first section of the filter is coated with plasticizer in that the toner particles are primarily retained in the first section and coating of the second higher density section may seal the filter.

The invention will be further described with reference to the accompanying drawing which is illustrative of the use of a filter of the invention in the form of a bag in the plate-cleaning station of a xerographic machine.

Referring now to the drawing, there is shown the platecleaning station of a xerographic machine, in which generally designates a xerographic plate including a layer 11 of photoconductive insulating material on a conductive backing 12 formed in the shape of a drum, which is suitably journaled for rotation in the direction indicated by the arrow to cause the drum surface sequentially to pass a plurality of xerographic processing stations, including the plate-cleaning station shown, as is common in the xerographic art. The plate cleaning assembly, generally designated 13, comprises a rotatable brush 14 of such construction as to apply extremely light pressure to the photoconductive surface of the xerographic drum to dislodge any particles of toner that may adhere thereto. The brush 14, is cleaned by a flicking bar 15 that is mounted within the hood 16 to contact the ends of the brush bristles, as they rotate, to detach particles of toner adhering thereto. The hood 16 encompasses approximately three-fourths of the brush area and is used for containing 4 the particles of toner removed from the drum by the brush and by the flicking bar from the brush.

An elongated exhaust duct 17 is arranged to cover a slot that extends transversely across the hood 16 to permit the removal of dust particles from the hood, the exhaust duct protruding into a filter box 18 that is attached to the hood 16. The motor-driven centrifugal blower 19 connected by conduit 20 to the filter box produces a flow of air through the filter box, drawing air through areas surrounding the xerographic drum and the hood, the air entraining particles of toner removed from the xerographic drum by the brush and by the flicking bar from the brush. Toner particles are separated from the air as it passes through the filter box by a filter bag 25, formed in accordance with the invention, and attached to the exhaust duct 17 so that only clean air reaches the motordriven centrifugal blower 19.

The filter bag 25 is formed from fiber glass and has an inner wall 28 of progressively increasing density and an outer wall 27 of substantially uniform density, the denser side of wall 28 being positioned against wall 27. In accordance with the invention the fibers of inner wall 28 are coated with a plasticizer for the toner.

The filter bag, formed of fiber glass coated with a. plasticizer for the toner, employed in the plate-cleaning station, is preferably constructed as a self-supporting filter bag in accordance with the teachings of U.S. Patent 3,252,274 to Benson et al., hereby incorporated by reference, whereby the toner particles travel through a filter medium of progressively increasing density and then through a filtering medium of substantially uniform density. The filter bag may be monted in the filter box in accordance with the teachings of U.S. Patent 3,410,060 to Reilly et al., hereby incorporated by reference.

It is to be understood that the teachings of the invention are equally applicable to filters constructed and mounted in a filter box of a xerographic machine in a manner other than as described in the aforementioned patents and therefore the scope of the invention is not limited by the particular structure disclosed in such patents. Thus, for example, the teachings of the invention are equally applicable to filters which are not self-supporting; e.g., a fiber glass liner supported within a suitable filter support constructed of, for example, perforated cardboard or sheet metal. In such filters, the fiber glass preferably has a density gradient whereby the toner particles pass through a progressively increasing density of fiber glass.

Similarly, as hereinabove noted, the filter may be constructed of a material other than fiber glass and may be employed in a form other than a bag. Furthermore, the teachings of the invention are not limited to filters used in the cleaning station of a xerographic machine. Thus, as should be apparent from the hereinabove description, the teachings of the invention are generally applicable to increasing the efiective life of filters to be used for separating toner material.

The invention is further illustrated by the following example, but the scope of the invention is not to be limited thereby.

EXAMPLE A fiber glass blank having a weight of 8 to 10 grams per square foot and a progressively increasing density, is impregnated with dioctyl phthalate to uniformly coat the fiber glass fibers. The blank is about /z inch thick and is cut to the dimensions of a filter bag comprised of fiber glass having a density of 1 pound per cubic foot and a thickness of /2 inch. The blank is inserted into the bag and employed in the cleaning system of a xerographic machine, employing a tone'r comprising a styrenen-butyl methacrylate copolymer, polyvinyl butyral and carbon black, produced by the method disclosed by M. A. Insalco in Example I of U.S. Pat. 3,079,342.

The filter bag performs effectively after the production of 18,000 prints.

The filters of the invention are an improvement over the filters presently employed for separating toner particles in that the toner particles which are deposited on and in the filter are plasticized; i.e., the toner particles lose their particulate nature, whereby the filter material is coated with plasticized toner. The plasticization of the toner increases the useful life of the filter by increasing the filter surface area available 'for deposition of toner particles and preventing filter blockage caused by a buildup of toner particles. The use of a plasticized filter in a Xerographic machine is found to increase the useful life of the filter from about 4,000 copies to about 18,000 copies or more; i.e., the filter operates without a significant pressure drop up to 18,000 copies or more.

Numerous modifications and variations of the invention are possible in light of the above teachings and therefore the invention may be practiced otherwise than as particularly described.

What is claimed is:

1. In the vacuum cleaning system of a Xerographic machine including an exhaust duct through which air entrained toner particles flow and a filter for separating the toner particles connected to the exhaust duct, the improvement for increasing the useful life of the filter comprising: said filter being coated with a plasticizer for said toner, said plasticizer being present in. an amount sufiiicent to cause said toner particles retained by the filter to lose their particulate shape.

2. The vacuum cleaning system of a xerographic 6 machine as defined in claim 1 wherein the filter is comprised of fiber glass.

3. The vacuum cleaning system of a Xerographic machine as defined in claim 2 wherein the filter is a bag having the interior thereof in fluid flow communication with the duct, said bag being comprised of an inner wall of fiber glass material of progressively increasing density and an outer wall of substatnially uniform density having a density greater than the maximum density of the inner wall, the inner wall being coated with the plasticizer.

References Cited UNITED STATES PATENTS 1,521,575 12/1924 Wittemeier VCSUX 1,829,618 10/1931 Studer 55524X 2,353,936 7/1944 Smith 55VCSUX' 2,579,984 12/ 1951 Trowbridge 55--VCSUX 2,733,776 2/1956 Garelick 55-524 3,133,884 5/1964 Graham et al. 55524X 3,221,480 12/1965 Stefcik et a1. 55524 3,246,655 4/1966 Spears et a1 131-10 3,252,274 5/1966 Benson et al 55382X 3,284,361 11/1966 Rocchini et a1 25288 DENNIS E. TALBERT, 111., Primary Examiner US. Cl. X.R. 

